Effects of Protonation State on Electrocatalytic CO 2 Reduction by a Cobalt Aminopyridine Macrocyclic Complex
Effects of Protonation State on Electrocatalytic CO 2 Reduction by a Cobalt Aminopyridine Macrocyclic Complex
复制标题
质子化状态对钴氨基吡啶大环配合物电催化CO 2 还原的影响
DOI：
10.1021/acs.inorgchem.1c01977
复制
发表时间：
2021
影响因子：
4.6
通讯作者：
Marinescu, Smaranda C.
中科院分区：
文献类型：
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作者：
Liu, Jeffrey J.;Chapovetsky, Alon;Haiges, Ralf;Marinescu, Smaranda C.
在CO2还原为CO和H2O的过程中，一个关键的组成部分是将2当量的质子和电子传递给CO2分子。这些质子和电子转移步骤的时间和顺序是指导催化CO2还原的活性和选择性的重要因素。在以前的研究中，我们已经报道了一系列的大环氨基吡啶钴配合物能够还原CO2 CO与高法拉第效率。动力学研究揭示了所观察到的速率常数（Kobs）和侧胺氢键供体的数量减一之间的关系，这表明存在去质子化的活性催化状态。在这里，我们调查的可行性，这些建议去质子化的配合物对CO2还原。合成了四氨基大环Co（L）的两个去质子化衍生物Co（L4-）和Co（L2-），并对其结构进行了表征，发现去质子化后负电荷发生了广泛的离域.核磁共振谱和紫外-可见滴定研究证实，在催化条件下，催化剂的活性形式逐渐变成去质子化的，从而支持了thendonor- 1与kobs的关系. Co（L4-）的电化学研究表明，这种去质子化的类似物在加入外源性弱酸源（如2，2，2-三氟乙醇）时能够进行电催化，导致CO2-至-CO转化的法拉第效率与用完全质子化的衍生物观察到的那些相同（>98%）。
A critical component in the reduction of CO2to CO and H2O is the delivery of 2 equiv of protons and electrons to the CO2molecule. The timing and sequencing of these proton and electron transfer steps are essential factors in directing the activity and selectivity for catalytic CO2reduction. In previous studies, we have reported a series of macrocyclic aminopyridine cobalt complexes capable of reducing CO2to CO with high faradaic efficiencies. Kinetic investigations reveal a relationship between the observed rate constant (kobs) and the number of pendant amine hydrogen bond donors minus one, suggesting the presence of a deprotonated active catalytic state. Herein, we investigate the feasibility of these proposed deprotonated complexes toward CO2reduction. Two deprotonated derivatives,Co(L4–)andCo(L2–), of the tetraamino macrocycleCo(L)were independently synthesized and structurally characterized revealing extensive delocalization of the negative charge upon deprotonation.1H nuclear magnetic resonance spectroscopy and ultraviolet–visible titration studies confirm that under catalytic conditions, the active form of the catalyst gradually becomes deprotonated, supporting thus thendonor– 1 relationship withkobs. Electrochemical studies ofCo(L4–)reveal that this deprotonated analogue is competent for electrocatalysis upon addition of an exogenous weak acid source, such as 2,2,2-trifluoroethanol, resulting in faradaic efficiencies for CO2-to-CO conversion identical to those observed with the fully protonated derivative (>98%).